Carburettors

ABSTRACT

The invention provides an air valve carburettor wherein the contoured needle is mounted for axial movement relative to the suction operated member and temperature sensitive control means are provided and associated between said contoured needle and said suction operated member whereby the cross sectional area of the jet orifice is determined by the temperature sensed by the temperature sensitive control means which temperature will be influenced inter alia by the temperature of the incoming fuel, the temperature of the air passing beneath the air valve and the temperature of the engine.

United States Patent [151 3,653,642

Lawrence 1 51 Apr. 4, 1972 1 CARBURETTORS 3,100,236 8/1963 0:: et a1 ..261/s1 x 3,273,868 9/1966 Morton ..261/50 AA [72] inventor: Geollrey Lloyd Lawrence, Potters Bar, En- 3,309,069 3/1967 Bram at al 261/50 AA 3,333,832 8/1967 O'Neill. 261/50 AA 73 A The Zenith Car-bumm- C m 3,350,071 10/1967 Scala, Jr ..26l/34 B l 1 summon, Middlmx a 3,362,694 1/1968 Gould ....261/50 AA 3,484,084 12/1969 Simpson et a1 .....261/52 X [22] Filed: Oct. 16, 1969 Primary Examiner-Tim R. Miles [2]] Appl' 866'939 Attorney-Larson, Taylor and Hinds Foreign Application Priority Data [57] ABSTRACT Oct. 22, 1968 Great Britain ..50,l04/68 The invention provides an air valve carburettor wherein the contoured needle is mounted for axial movement relative to [52] US Cl 261/39 5, 261/44 R, 26|/50 AA the suction operated member and temperature sensitive con- [51] lnt.Cl ..F02n1 U10 "Walls Provided and associawd bflween Said 53 n w 0| s 2 1 "39 B 44 R toured needle and said suction operated member whereby the cross sectional area of the jet orifice is determined by the tem- [56] 'cm perature sensed by the temperature sensitive control means which temperature will be influenced inter alia by the tem- UNITED STATES PATENTS perature of the incoming fuel, the temperature of the air passing beneath the air valve and the temperature of the enl,l58,359 10/1915 Abell ..261/50 AA sine. 1,433,689 10/1922 Tracy et a1. .....261/50 AA 1,830,562 11/1931 Robbins ..261/50 AA 4 Claims, 2 Drawing Figures CARBURETTORS This invention relates to carburettors for internal combustion engines of the kind hereinafter referred to as an air valve carburettor" wherein a fuel metering jet is provided the cross sectional area of which is controlled by acontoured needle in dependence upon the positionof a suction operated member that controls the effective cross sectional area of a choke in the air passage of the carburettor.

An air valve carburettor is known in which the suction operated member is a piston which carries said contoured needle wherein a temperature responsive device is incorporated which at low throttle opening lifts the piston so that the contoured needle is moved axially in relation to the fuel metering jet. It is also known to provide a cold starting device in which the jet is moved axially by a manual control away from the needle to increase the cross sectional area of the jet without lifting the piston, and so provide an enriched mixture to ensure easy starting and even running when the engine is cold.

According to the present invention there is provided an air valve carbutettor wherein the contoured needle is mounted for axial movement relative to the suction operated member and temperature sensitive control means are provided and associated between said suction operated member and said contoured needle. Said air valve carburettor may have a suction operated member constituted by a piston with which the contoured needle is assembled for axial relative movement by said temperature sensitive control means which may be a bi-metallic strip and said bi-metallic strip may be secured to said piston. The contoured needle may be mounted in a holder member slidably mounted in said piston and said needle may be yieldably mounted for axial movement in said holder against the action of a coil spring. The holder may be made of nylon or other anti-friction plastics material providing relatively free movement and good wearing qualities.

REF ERRING TO THE DRAWINGS FIG. 1 is a sectional view of one form of air valve carburettor made in accordance with the present invention; and

FIG. 2 is a fragmentary sectional view to an enlarged scale of the lower part of the air valve and contoured needle shown in FIG. 1, said section being turned through 90 with respect to FIG. 1. I t

Referring to FIG. 1 there is illustrated an air valve carburettor generally designated 1 1 consisting of a body 12, a cover assembly 13, and a fuel chamber 14. A mixture passage 16 providing at its extremities an air intake 17 and a mixture outlet 18 is formed in the body 12. There'is provided intermediate the passage extremities, a contoured restriction 19 which is designed to have predetermined contours shown as the inclined anterior and posterior approaches 21 and 22, respectively, separated by a substantially flat rectangular median bridge portion 23 commonly referred to as a bridge as it connects the inclined surfaces 21 and 22. The contoured restriction 19 extends over a portion of the length of the mixture passage 16 with the width of the bridge portion 23 being substantially parallel to and spaced from the axis of the passage. A throttle valve 24 in the mixture passage adjacent the outlet extremity 18 controlled by the engine operator in the usual manner is rotatably supported on the'throttle shaft 26 journailed in the body to control the introduction'of the fuel/air I mixture to the engine manifolding (not shown). 7

The fuel chamber 14 depends from the body 12 Fuel is supplied to the fuel chamber through an inlet (not shown) and is controlled in a normal manner by a float actuated valve (not shown). Supported in a cylindrical cavity 31 formed as a part of the body immediately below the bridge 23 is the fuel jet assembly generally indicated as 32. The jet assembly extends into the fuel chamber 14 and the major portions of the assembly are surrounded by fuel.

The jet assembly 32 consisting of a bushing 33 fixedly secured in the body 12, extends upwardly through an aperture 34 centrally disposed in the bridge and opens into the mixture passage. A hollow screw threaded closure plug 36 extends through an appropriately located opening 37 formed in the bottom of the fuel chamber 14 with an 0" ring 38 providing a sealing means therebe tween. A tubular member 39 is fixedly positioned in the bushing 33 extends downwards into the fuel chamber 14. An orifice 40 at the top of the bushing 33 opens at the surface of the bridge to provide a metering orifice or jet.

Fuel from the chamber 14 will flow through the tubular member 39 to the jet at the bridge in the mixture passage. Metering of the fuel flow from the orifice will hereinafter be more fully described.

Formed as a part of the body 12 and opening upwardly from the mixture passage 16 is a substantially inverted conical structure 53 which combines with the cover assembly 13 to define a compartmented chamber generally designated as 54. Slidably supported within the chamber 54 and the mixture passage 16 is a piston 56 commonly referred to as the air valve. The piston slidably engages in the opening 57 between the mixture passage and the conical structure. The opening 57 is immediately above the bridge 23. A flexible diaphragm 58 at its inner periphery is clamped between the piston 56 and a diaphragm retaining washer 59. The outer periphery of the diaphragm is clamped between the mating flanges 61 and 62 of the cover assembly 13 and the conical structure 53, respectively, thus dividing the chamber 54 into a suction chamber 63 and a reference pressure chamber 64.

A piston shaft 66 integral with the piston 56 extends up-v wardly through the piston cavity 67 into sliding engagement with the bushing 68 and a guide bore 69 formed in the ribbed cover 13 to accurately guide the piston movements toward and away from the bridge. A light piston compression spring 71 confined between the cover 13 and the bottom wall .of the piston cavity 67 urges the piston towards the bridge 23. The pressure drop created by the air flow between the bridge and the base of the piston is communicated to the suction chamber 63 by an opening 72 formed in the base of the piston; thus the induction pressure existingin the mixture passage 16 between the throttle valve 24 and the contoured restriction 19 are communicated via the opening 72 and the piston cavity 67 to the suction chamber 63. A reference pressure, usually atmospheric pressure, is communicated to the reference chamber 64 by a passage 73. This passage in the present embodiment is vented to the air entrance through the air filter means (not shown) to prevent the ingress of undesirable foreign matter. The passage 73 may if desired be vented directly to the atmosphere, or into the air intake passage 17, or alternatively the passage may comprise a plurality of channels in combination communicating with the air intake 17 and the atmosph'cre.

Operatively connected to the piston 56 is a tapered metering needle 74 (FIG. 2) which projects into the fuel orifice 40 to regulate the effective orifice area subject to the substantially constant vacuum created by the constant air velocity to restrict the fuel flow therefrom. The manner in which the needle 74 is mounted will be described later with reference to FIG. 2.

Means in the form of punctiform projections (not shown) are provided on the bottom face of the piston 56 in a position to contact the bridge and establish a minimal spatial separation'between the piston 56 and the bridge 23. The function served by the punctiform projections could, of course, be accomplished by adjusting set screws (not shown) positioned in the body or conical structure adapted to engage the piston during its movement to establish the lower limits of piston travel. I

Referring again to FIG. 2 it will be seen that the contoured needle 74 is provided with an enlarged flat topped head and is slidably carried in a bore 101 provided in a holder 102 which in turn is slidably mounted in a cylindrical recess 104 formed in the base of the piston 56 said holder being made of metal or plastics material. A coil spring 106 located in the bore 101 is engaged beneath the head 100 and an inturne'd flange 107 formed at the bottom of the holder 102 the needle 74 being retained in the bore 101 by a disc 108 inserted in the top of the holder 102 (after the needle has been inserted) and engaged with an internal annular groove 110 provided in said bore. The washer 108 has an eccentrically positioned downwardly extending projection 109. Near the base of the holder 102 there is provided a peripheral groove 111 shown engaged by the outer end of a bimetallic strip 1 12 secured in a rebate 114 formed in the base of the piston 56 by a screw 1 l6. Adjustment of the mounting of the bimetallic strip 112 is provided by a stud 118 secured in the piston 56 and a nut 120 engaged with said stud 118. It is to be noted that the shaft 122 of the needle 74 which lies within the holder 102 is cylindrical and is of less diameter than the bore in the flange 107 so that the needle can make a limited angular movement within the bore 101. The function of the spring 106 being to hold the needle 74 pressed up against the projection 109 so that the needle 74 is urged to take up, at all times, a position inclined in a predetermined plane to the axis of the orifice member 39, so that it at all times contacts the side of the orifice at a chosen position and the flow characteristics of the orifice are not altered by changes of position of the needle in the cross sectional plane of the orifice.

In operation it will readily be understood that the temperature sensitive bimetallic strip 112 will control the position of the needle 74 relative to the piston 56 according to the temperature to which said strip is subjected, which temperature will be influenced inter alia by the temperature of the incoming fuel contacting the needle 74 "and by the temperature of the air passing beneath the air valve 56 which inturn is always to a greater or less extent influenced by engine temperature.

lclaim:

1. An air valve carburettor having an air passage, a choke in said air passage, a piston controlling the effective cross sectional area of said choke, said piston moving transversely of said air passage, a fuel metering orifice opening into said air passage, a contoured needle carried by said piston and movable axially in said orifice, means coupling said needle to said piston, a temperature sensitive control means connected between said needle and said piston and situated in the vicinity of the fuel discharge in said air passage, said needle being mounted in a holder and said holder being slidably mounted on said piston, said holder being moved relative to said piston by said temperature sensitive control means.

2. An air carburettor according to claim 1 wherein yieldable support means is provided between said needle and said holder.

3. An air valve carburettor according to claim 1 wherein said temperature sensitive control means is a bimetallic strip mounted on said piston and carrying said holder.

4. An air valve carburettor according to claim 1, further including means for biassing said contoured needle towards the wall of said fuel metering orifice. 

1. An air valve carburettor having an air passage, a choke in said air passage, a piston controlling the effective cross sectional area of said choke, said piston moving transversely of said air passage, a fuel metering orifice opening into said air passage, a contoured needle carried by said piston and movable axially in said orifice, means coupling said needle to said piston, a temperature sensitive control means connected between said needle and said piston and situated in the viciNity of the fuel discharge in said air passage, said needle being mounted in a holder and said holder being slidably mounted on said piston, said holder being moved relative to said piston by said temperature sensitive control means.
 2. An air carburettor according to claim 1 wherein yieldable support means is provided between said needle and said holder.
 3. An air valve carburettor according to claim 1 wherein said temperature sensitive control means is a bimetallic strip mounted on said piston and carrying said holder.
 4. An air valve carburettor according to claim 1, further including means for biassing said contoured needle towards the wall of said fuel metering orifice. 